Today I came to know that vs2017 does not support development of apps for windows Phone 8.1. They suggest to run it in VS15. It is a very bad news there are many windows Phone 8.1 users. So if I want to develop app and want to use new features of VS 17 I should install 2 Vs. It looks very bad. Current creators update sdk runs only in vs17 so for that we need vs17 and this vs15.